Project Summary/Abstract Vaccination is essential to the global fight against infectious diseases. However, some pathogens are experts at evading the immune response, and therefore present a challenge to current vaccination strategies. Influenza vaccination is currently only 60% effective, and depends on proper predictions of influenza strains that will become seasonal epidemics every year. HIV vaccination has been unsuccessful thus far, with some vaccine trials resulting in adverse outcomes. Traditionally, vaccine design focuses on eliciting memory responses by effector cells of the adaptive immune system. However, it is unknown how cells of the innate immune system respond to vaccination, and whether they play a role in successful vaccine responses. Natural killer (NK) cells are effector cells of the innate immune system that respond rapidly to viral infection. In this proposal, we aim to determine the effect of influenza or HIV vaccination on NK cells. We will deeply interrogate the NK cell response to vaccination by using mass cytometry, an innovative new technology that allows the analysis of 40+ protein expression parameters simultaneously at the single cell level. This method will allow us to analyze clinical samples from influenza and HIV vaccine studies in great depth. Additionally, we will determine the cell biological mechanisms involved in generation of a diverse and functional NK repertoire by analyzing the genome-wide epigenetic profiles of NK cells that respond to vaccination and viral infection. This will allow us to define signatures of NK cell maturation, activation, and diversification. These studies will deepen our understanding of the innate immune response to vaccination, which will lay the foundation for future vaccine designs that incorporate both the innate and the adaptive immune systems.